The present invention relates to an optical disk device that performs recording or playback of information on an optical disk.
One cause of a servo track-following error in an optical disk device is a periodical disturbance that is caused with the rotation of an optical disk. Conventionally, the process of iterative learning control is known as one process or method of improving the track—following performance against the periodical disturbance. According to Japanese Unexamined Patent Application Publication No. 2002-140876, the iterative learning control refers to the process of control in which a servo error signal is delayed (or lagged) by a rotation period of the optical disk and then is summed to an un-delayed servo error signal, and the summed signal is supplied as a new servo error signal to a stabilization compensator. In addition, there is disclosed a configuration in which a digital memory is used. More specifically, in the disclosed configuration, the signal is stored into the digital memory in units of either an equal time period or a rotation angle of the optical disk, and the signal is delayed and output corresponding to the time period or the rotation angle of the optical disk.
Further, there is known a technique where low pass filter is provided that removes high frequency components contained in the servo error signal, in which a signal passed through the low pass filter is delayed and summed to a servo error signal not passing through the low pass filter, thereby to secure stability.